In a continuous casting process for steel, for example, application of a direct current magnetic field to molten steel discharged into a casting mold is performed for the purpose of quality improvement of a cast. It is known that a counterflow toward the direction opposite to a main stream is generated around a discharge flow of molten steel in this direct current magnetic field.
In normal continuous casting of molten steel, as shown in FIG. 7 for example, a submerged entry nozzle 102 which discharges molten steel 100 into a casting mold 101 is used. Discharge holes 103 which are pointed downward with respect to the horizontal direction are formed at two locations in the vicinity of a lower end of a side face of the submerged entry nozzle 102. Also, in order to clean the inside of the submerged entry nozzle 102, the molten steel 100 is discharged into the casting mold 101 from the discharge holes 103 while blowing non-oxidized gas such as Ar gas (argon gas). In a case where a direct current magnetic field is applied to a discharge flow 104 of the molten steel 100 discharged from the discharge holes 103 by for example an electromagnetic brake device (not shown), a counterflow 105 in the opposite direction is generated around the discharge flow 104. As a result, Ar gas bubbles 106 contained in the discharge flow 104 do not easily deeply enter the molten steel 100 within the casting mold 101 due to this counterflow 105. As a result, the number of the Ar gas bubbles 106 can be reduced inside a cast obtained by casting the molten steel 100.
However, since the Ar gas bubbles 106 flow on the counterflow 105 which rises along the submerged entry nozzle 102, is concentrated around the submerged entry nozzle 102 and floats to a meniscus 107, the bubbles may not be removed by the meniscus 107. In this case, some of the Ar gas bubbles 106 are trapped by a solidified shell 108 formed on the internal surface of the casting mold 101. As a result, the number of the Ar gas bubbles 106 in the surface layer of a cast obtained by casting the molten steel 100 is increased.
Thus, in order to prevent the Ar gas bubbles 106 from being trapped by the solidified shell 108 of the casting mold 101, electromagnetically stirring the molten steel 100 in the vicinity of the meniscus 107 in the upper part of the casting mold 101 is proposed. With this electromagnetic stirring, a stirring flow 109 is formed as shown in FIG. 8 for example, in the molten steel 100 in the vicinity of the meniscus 107; therefore, the Ar gas bubbles 106 trapped by the solidified shell 108 can be reduced (refer to Patent Document 1).
[Prior Art Documents]
[Patent Documents]
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2000-271710